1. Field of the Invention
This invention relates to medical devices and methods and more particularly relates to electrosurgical jaw, probe and needle structures with at least one polymer positive temperature coefficient of resistance (PTC) body portion for sensing tissue temperature and modulating ohmic tissue heating together with multiple circuitry components for intraoperative control of voltage applied to the engaged tissue.
2. Description of the Related Art
In the prior art, various energy sources such as radiofrequency (RF) sources, ultrasound sources and lasers have been developed to coagulate, seal or join together tissues volumes in open and laparoscopic surgeries. The most important surgical application relates to sealing blood vessels which contain considerable fluid pressure therein. In general, no instrument working ends using any energy source have proven reliable in creating a “tissue weld” or “tissue fusion” that has very high strength immediately post-treatment. For this reason, the commercially available instruments, typically powered by RF or ultrasound, are mostly limited to use in sealing small blood vessels and tissues masses with microvasculature therein. The prior art RF devices also fail to provide seals with substantial strength in anatomic structures having walls with irregular or thick fibrous content, in bundles of disparate anatomic structures, in substantially thick anatomic structures, or in tissues with thick fascia layers (e.g., large diameter blood vessels).
In a basic bi-polar RF jaw arrangement, each face of opposing first and second jaws comprises an electrode and RF current flows across the captured tissue between the opposing polarity electrodes. Such prior art RF jaws that engage opposing sides of tissue typically cannot cause uniform thermal effects in the tissue—whether the captured tissue is thin or substantially thick. As RF energy density in tissue increases, the tissue surface becomes desiccated and resistant to additional ohmic heating. Localized tissue desiccation and charring can occur almost instantly as tissue impedance rises, which then can result in a non-uniform seal in the tissue. The typical prior art RF jaws can cause further undesirable effects by propagating RF density laterally from the engaged tissue thus causing unwanted collateral thermal damage.
The commercially available RF sealing instruments typically adopt a “power adjustment” approach to attempt to control RF flux in tissue wherein a system controller rapidly adjusts the level of total power delivered to the jaws' electrodes in response to feedback circuitry coupled to the electrodes that measures tissue impedance or electrode temperature. Another approach used in the prior art consists of jaws designs that provide spaced apart of offset electrodes wherein the opposing polarity electrode portion s are spaced apart by an insulator material—which may cause current to flow within an extended path through captured tissue rather that simply between opposing electrode surfaces of the first and second jaws. Electrosurgical grasping instruments having jaws with electrically-isolated electrode arrangements in cooperating jaws faces were proposed by Yates et al. in U.S. Pat. Nos. 5,403,312; 5,735,848; and 5,833,690. In general, the prior art instruments cannot reliably create high strength seals in larger arteries and veins.